The present invention relates to overhead conveyors, which typically comprise at least an “I beam” track, trolleys which have opposed wheels engaging the bottom flanges of said I beam track on opposite sides of the center web of the beam, and a driven conveyor chain connected to said trolleys at spaced intervals. The chains usually comprise center links alternating with a pair of side links, which overlap the end of the center link on the opposite, sides thereof, and are joined to the center link by a pin passing through the overlapping ends of the side links and center links.
In accordance with long standing industry practice, the links of said chains come in lengths giving them a nominal 2 inch, 3 inch, 4 inch or 6 inch pitch dimension. The pitch is the distance between the centers of adjacent pins, and is referred to as nominal, as the pitch is typically 1/16 of an inch more than the nominal number. The actual length of each chain link is long enough to provide for the overlap, and leave the nominal pitch dimension as indicated. Chains are identified in part by their pitch. Thus a chain with a two inch pitch is referred to as a 2 inch chain, and so or By industry standard, a 2 inch chain uses pins which are 2/8 (¼) inch pins which are 4/8 (½) inch in diameter, and is more specifically identified as an X 348 chain. These and other dimensions for 2, 3, 4 and 6 inch chains are set forth in Table 1, with dimension “F” being the pin diameter. The other dimensions, A, B, C, etc listed in Table 1 are indicated in FIGS. 1 and 2. These are industry standards established through years of practice, and are set forth in the publications of the Conveyor Equipment Manufacturers Association (CEMA).
CEGHIChainABmaxDmaxFminminminX-2282 15/32 11/16⅜1⅛¼ 53/641 1/16 5/16X-50-6 (50)(11.90)(17.46) (9.53)(28.57) (6.35)(21.03)(26.98) (7.94)X-3483¾1 3/32½1 27/32½1 9/321⅝ 9/16X-75-13 (75)(19.05)(27.78)(12.70)(46.83)(12.70)(32.54)(41.27)(14.28)X-458411 13/32⅝2¼⅝1⅝2¼ 11/16X-100-16(100)(25.4)(35.71)(15.87)(57.15)(15.87)(41.27)(57.15)(17.46)X-67861 9/322 13/163-118⅞2¼3-318 31/32X-150-22(150)(32.50)(50.80)(20.63)(79.37)(22.22)(57.15)(85.72)(24.61)
Trolleys are connected to the driven chains by a depending leg which passes through the opening in a center link. Thus, trolleys can be spaced as close as nominally 4 inches for a two inch chain, or in multiples thereof. For a three inch chain, the spacing would be six inches or multiples thereof, for a four inch, eight inches or multiples and for a six inch, 12 inches or multiples thereof.
Also by industry standards and practice, the pitch of the chain used matches the nominal height of the I beam track used. The height of the beam may be higher than its nominal value, e.g. the actual height of a 2 inch beam is 2⅝ inches. Also by industry standard and practice, trolleys are referred to by their nominal wheel diameter, which corresponds to the nominal height of the beam track they are carried on. The actual diameter is slightly less than the actual height of the I beam, so there is no binding of the trolley wheel between the lower beam flange and the upper beam flange. Thus a trolley with a nominal wheel diameter of 2 inches is used on a nominal 2 inch beam, a nominal 3 inch diameter wheel trolley is used on a nominal 3 inch beam, a 4 on a 4, and a 6 on to 6.
Further, chains made to the various pitches are by practice and industry standard fashioned and manufactured to dimensions and pin sizes which cause the chain to have industry specified maximum allowable “chain pull loads.” Chain pull load refers to the load placed on the chain as it pulls its associated trolleys and any loads they are carrying. Thus, a 3 inch chain has a maximum allowable chain pull load of 1500 pounds. For a 4 inch chain it is 3000 pounds, and for a six inch chain, 5500 pounds.
Trolleys are referred to by their nominal wheel diameter, which by industry standard and practice corresponds to the nominal beam height. The drive chain is driven by one or more drives. Multiple drives must be synchronized, and are used to make sure the maximum chain pull load for the chain is not exceeded in any portion thereof.